The present invention relates to probes for measuring the properties of a stream of fluid.
The measurement of fluids is important in many areas of science. For example, knowledge of the fluid properties is important in the fluid flows inside turbomachines (for example jet engines and pumps), in the fluid flows over aircraft or road vehicles and in the fluid flows inside pipes or ventilation ducts.
The fluid properties in flows of gases and liquids of interest include: flow direction, pressure, temperature, speed, concentration of constituent parts. The fluid flows may have particles or droplets suspended in the flow, in which case it may be desirable to determine the size, the speed or the number per unit volume of the particles or droplets. There is also interest in the measurement of unsteady flows such as those found in turbomachines or in pipes, as well as the measurement of steady fluid flows.
It is often desirable to measure the properties of the flowing fluid at a known distance from the surface of the subject over which it is flowing. Known probes for this purpose comprise an elongate probe with the sensing head i.e. the part which is exposed to the fluid flow located at a distal end thereof to provide the desired spacing of the sensing surface of the probe from the surface of the subject of interest over which the fluid flows.
Conventional probes have sensing heads based on three-dimensional aerodynamic shapes. Examples are sensing heads having hemispherical sensing surfaces, and frusto-conical and multi-faceted frusto-pyramid sensing surfaces where the apexes are pointed toward the oncoming flow.
Multiple measurements are required when more than one quantity is to be determined. The probes discussed above all employ a sensing head having a plurality of surfaces each provided with an associated sensor and facing in different directions, such as the hemispherical sensing head, the frusto-conical sensing head and the multi-faceted frusto-pyramid sensing head, in order to determine the direction of the fluid flow by comparing the signals from the sensors associated with each of the surfaces.
The present invention was based on the finding that the flow direction of a fluid and other flow properties of a fluid can also be determined using a probe having a planar sensing surface with a plurality of sensors at different positions of the planar sensing surface.
According to a first aspect of the present invention, there is provided an elongate probe for measuring one or more properties of a stream of fluid, the probe having an external planar sensing surface, which in use is exposed to the stream of fluid, at a longitudinal end thereof and comprising a plurality of sensors at the planar external sensing surface.
According to a second aspect of the present invention there is provided the use of the above elongate probe for measuring one or more properties of a stream of fluid.
According to a third aspect of the present invention, there is provided a method of measuring one or more properties of a stream of fluid using the above elongate probe, the method comprising positioning the probe in the stream of fluid such that the stream of fluid flows directly over the external planar sensing surface.
The sensors are preferably located such that the sensitive element of each sensor lies in or substantially in the plane of the planar sensing surface. This reduces the time for the sensors to respond to changes in the flow properties of the fluid, which is particularly important for detecting transient flow changes. The sensitive elements of the individual sensors may be placed flush with the external planar sensing surface, or alternatively, they may be placed within the body of the sensing head just below the sensing surface, or placed just above the sensing surface.
The feature that the sensing surface is planar does not exclude the provision of flow manipulation microstructures on the planar sensing surface, provided that such structures do not significantly affect the response time of the sensors. The advantages of providing such flow manipulation microstructures are discussed in detail below.